1. Field of the Invention
This invention relates generally to a new and improved method and apparatus for picture data transmission, picture processing and a recording medium and, more particularly, to a new and improved system for real-time display of a three-dimensional object responsive to a user input or processing results achieving moderate precision, with the use of relatively limited hardware resources, such as a video game machine or a personal computer whereby greater efficiency at lower cost is accomplished.
2. Description of the Related Art
In a typical TV game machine for household use, a personal computer or a graphics computer, a picture processing device designed for generating picture data outputted to a TV receiver or a monitor receiving data for display, is made up of a general-purpose memory, a CPU and other processing LSIs, interconnected over a bus. A dedicated picture drawing device is provided between the CPU and a frame buffer looking in the direction of the flow of picture data for drawing to facilitate high-speed processing.
In the aforedescribed system, the CPU does not have direct address to a frame buffer as a display memory associated with a display screen. Instead, the CPU performs geometry processing, such as coordinate transformation, clipping or light source calculations, for defining a three-dimensional model as a combination of basic unit figures (polygons) such as triangles or quadrangles, to produce a command for drawing a three-dimensional picture. The CPU sends the picture drawing command over an external bus to a suitable drawing device.
The drawing command includes information such as the shape, position, direction, color or the pattern of the polygon to be drawn. The shape, position or the direction of the polygon is determined by the coordinates of the polygon apex points.
For displaying a three-dimensional object, the object is first analyzed into plural polygons. The CPU produces a drawing command for each of these polygons. The drawing commands so generated are then transmitted over a bus to a picture drawing device which executes the drawing commands in order to write display data in the frame buffer for displaying the targeted three-dimensional object.
For representing the object more realistically, a technique known as a texture mapping or mip mapping is used, in which a pre-set picture pattern is readied and the inside of the polygon is modified using the picture pattern.
There is also a well-known technique of varying the display color by converting the color data of a picture through a color lookup table (CLUT) having color lookup data recorded thereon.
In the TV game machine for domestic use or a processing LSI making up a personal computer, attempts have been made to improve performance by speeding up the operating frequency or reducing the circuit scale without increasing the cost. However, the usual capacity of a low cost general-purpose memory is not increased significantly by incoming speed of operation. Hence, in a TV game machine for household use, or in a personal computer, the memory capacity proves to be a bottleneck.
In particular, for texture mapping using a high-quality picture prepared in advance in a high-quality work station (pre-rendering pattern) as a texture pattern, it is necessary to hold all patterns making up a segment of a moving picture in a memory. However, in this case, the higher the resolution of the texture pattern, the more significantly the available memory capacity is curtailed.
Consequently, a method is employed for holding the texture pattern in a compressed form in a memory and reading out the data of the compressed texture pattern each time the data is used and of expanding (de-freezing) the compressed data using a dedicated picture expansion device.
By way of example, a typical texture pattern is made up of picture data of a picture area dimensioned 64 vertical pixels by 64 horizontal pixels. However, since the texture pattern is not necessarily rectangular in shape, pixels not drawn, that is transparent pixels, need to be set in the picture data of the rectangular picture area for representing the required texture pattern.
Thus, in the drawing device, a method is required for discriminating these non-drawn pixels in the data of the texture of the rectangular area. To this end, the information termed an .alpha.-plane, of the same screen area for representing transparency is provided separately.
However, since the drawing device needs to perform processing for drawing using the .alpha.-plane, the information on the .alpha.-plane needs to be stored along with the texture picture data in the memory, thus necessitating increased memory capacity.
In order to avoid such increased memory capacity requirements, it has also been proposed to pre-set special values representing the transparency for each pixel value, such as (R, G, B)=(0, 0, 0) in the case where the pixel values are represented by three prime colors of red (R), green (G) and blue (B). The drawing device then does not rewrite the value of the frame buffer if the pixel value is the above value for the display picture, the pixel in the texture picture being then transparent.
However, high-efficiency compression for picture data, such as texture picture data, is generally irreversible, such that transparent portions occasionally may be decoded as being opaque, in which case such opaque pixel portions are displayed as noise at the peripheral edge of the texture pattern.
On the other hand, in a system in which a special value is used as a pixel value for representing transparency, and an opaque pixel is suddenly changed to a non-drawn transparent pixel, a jagged noise, or so-called aliasing noise, is occasionally produced in an edge of a texture pattern when a texture pattern is displayed to a reduced scale or to an enlarged scale. This is similar to the phenomenon which occurs in case of unsatisfactory picture synthesis employing a blue background of a chroma key in television broadcasting.
Accordingly, there has been a long existing need for improved methods and apparatus for overcoming the aforedescribed problem in which a high-quality picture, such as a pre-rendered texture pattern, provided as a picture, is deteriorated when it is drawn for display. The present invention clearly fulfills this need.